Treatment couch with localization array

ABSTRACT

Fiducial localization methods and apparatus are described.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/214,771, which claims the benefit of U.S. Provisional PatentApplication No. 60/936,388, which are hereby incorporated by reference.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of radiationtreatment, and in particular, to the positioning of an electromagneticlocalization array for use in image guided radiation treatment utilizingwireless transponders.

BACKGROUND

Radiotherapy and radiosurgery are non-invasive radiation treatmentoptions widely used to treat patients with a variety of tumors such asbrain tumor, lung tumor, and liver tumor. Fiducial tracking is one amonga variety of conventional tracking methods utilized in performingradiation treatments.

Electromagnetic tracking systems are used to track the positions offiducials in near real time (e.g., 10 Hz). In one type of system (i.e.,Calypso® 4D Localization System, available from Calypso, of Seattle,Wash.), an array of four transmitter coils spread out in space induces aresonance in a fiducial or transponder coil system. When the magneticfield is switched off, the transponder signal during relaxation issensed by an array of receiver coils and used to establish the positionof the transponder. In the Calypso 4D Localization System, thetransmitter and receiver coils are embedded in an array wired to acommon device, and the fiducials or transponders are wireless.

A tracking system may provide the positions of fiducials or transpondersthat are implanted in a patient before acquisition of a treatmentplanning computed tomography (CT) scan, for example for radiationtherapy. The fiducial positions are known relative to the transmittercoils or electromagnetic localization array. If the transmitter coil orarray position is known in the treatment room, the fiducial positionsrelative to the treatment room isocenter (treatment room coordinatesystem origin) can be obtained. The fiducial positions can then be usedto guide treatment, for example, by directing a radiation beam at atarget tracked by reference to the fiducial positions.

In such a tracking system, inappropriate placement of the localizationarray may cause problems such as susceptibility to interference in thearray or physical obstruction of other elements of the treatment system.

Another problem with electromagnetic tracking systems is that theaccuracy of the position and orientation information is affected bychanges in the magnetic field other than those created by thetransmitter coils. Perturbations in the magnetic field can be caused bythe presence of metal (for example, in radiation therapy, a gantry orrobotic manipulator and a linear accelerator) or other conductivematerial (for example, a treatment table top made out of conductivematerial). Thus the position information reported by an electromagnetictracking system in practical use, for example, tracking a target regioninside a patient during radiation therapy, can have a higher error thana system specification determined in a carefully controlled laboratorysetting.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1 illustrates a treatment delivery system including localizationarray for tracking implanted fiducials according to one embodiment ofthe invention.

FIG. 2 illustrates a localization array integrated within a treatmentcouch according to one embodiment of the invention.

FIG. 3A illustrates a localization array mounted underneath a treatmentcouch using a motorized attachment mechanism according to one embodimentof the invention.

FIG. 3B illustrates a localization array mounted underneath a treatmentcouch using a motorized attachment mechanism according to one embodimentof the invention where the localization array is positioned beyond animaging field of an imaging device.

FIG. 3C illustrates a localization array mounted underneath a treatmentcouch using a motorized attachment mechanism according to one embodimentof the invention where the localization array is rotated beyond animaging field of an imaging device.

FIG. 4 illustrates a localization array attached to a treatment couch byan attachment mechanism according to one embodiment of the invention.

FIG. 5 is a flow chart illustrating a process for using a localizationarray and treatment couch assembly according to one embodiment of theinvention.

FIG. 6 illustrates one embodiment of a treatment delivery system with anelectromagnetic tracking system capable of compensating for positionalinformation error.

FIG. 7 illustrates one embodiment of a localization array with embeddedfiducial markers.

FIG. 8 illustrates one embodiment of a treatment delivery system with anelectromagnetic tracking system capable of compensating for positionalinformation error.

DETAILED DESCRIPTION

Described herein is a method and apparatus for positioning alocalization array for use in image guided radiation treatment utilizingwireless transponders. The following description sets forth numerousspecific details such as examples of specific systems, components,methods, and so forth, in order to provide a good understanding ofseveral embodiments of the present invention. It will be apparent to oneskilled in the art, however, that at least some embodiments of thepresent invention may be practiced without these specific details. Inother instances, well-known components or methods are not described indetail or are presented in simple block diagram format in order to avoidunnecessarily obscuring the present invention. Thus, the specificdetails set forth are merely exemplary. Particular implementations mayvary from these exemplary details and still be contemplated to be withinthe spirit and scope of the present invention.

According to one embodiment of the present invention, a localizationarray to be used for tracking fiducial markers may be coupled with atreatment couch. For example, the localization array may be containedwithin or attached underneath or above the treatment couch. Such anarrangement may ensure that the localization array maintains itsposition with respect to the treatment couch, even if the treatmentcouch moves. Thus, the position of the localization array in thetreatment room can be tracked with reference to the treatment couch,rather than tracked independently.

Attachment of the localization array to the treatment couch may alsoeliminate the need for additional equipment or structures for supportingthe array. The presence of such equipment or structures in the treatmentroom may block imaging equipment, such as an x-ray imager, or mayphysically obstruct moving equipment, such as a robotic arm forpositioning a linear accelerator (LINAC). Accordingly, attachment of thelocalization array to the treatment couch may also reduce the likelihoodof collisions between these pieces of equipment.

Many approaches may be used to couple a localization array to atreatment couch at a desired position. For example, in one embodiment,the localization array may be contained within the treatment couch. Inother embodiments, the localization array may be mounted underneath orabove the treatment couch. Alternatively, the localization array mayalso be laid on top of the treatment couch. In this case, a patientundergoing radiation treatment may then lie on top of the localizationarray. A pad or other covering may be used to separate the patient andthe localization array.

The localization array may further be coupled to the treatment couchusing an attachment mechanism that allows the localization array to berepositioned while remaining attached to the treatment couch. In otherembodiments, the attachment mechanism may also allow the localizationarray to be detached from the treatment couch entirely and thenreattached to the treatment couch at a different location.

FIG. 1 illustrates a radiation treatment delivery system including alocalization array for tracking fiducial markers implanted in apatient's body, according to one embodiment of the invention. Treatmentdelivery system 100 includes robotic arm 101, linear accelerator (LINAC)102, treatment couch 104 for supporting patient 103, localization array105 for detection position of implanted fiducial markers 106, andprocessing unit 107.

Robotic arm 101 carries a LINAC 102 that is capable of producing a beamsuitable for use in radiation treatment. Robotic arm 101 is capable ofmaintaining the direction of the beam of LINAC 102 at a desired target,for example, a tumor within the body of patient 103. Robotic arm 101 mayalso respond to signals from a target tracking system, such asprocessing unit 107, to compensate for movement of the target during thetreatment process. Treatment couch 104 may be used to support the bodyof patient 103 during the treatment process and may be a robotictreatment couch. For example, the treatment couch 104 may be a roboticcouch capable of movement with at least five degrees of freedom.Alternatively, the treatment couch may be a robotic couch capable ofmovement with less than five degrees of freedom (e.g., four, three, orfewer degrees of freedom).

In an embodiment where the treatment couch can be repositioned using arobotic arm, the position of the treatment couch in the treatment roomcan be determined using mechanical encoders such as sensors attached tothe robot arm. The sensors may determine the position of the treatmentcouch and the localization array attached to the couch based on thejoint orientations of the robotic arm.

The treatment couch 104 may also respond to signals from a targettracking system to help compensate for movement of the target.Alternatively, treatment couch 104 may be another type of treatmentcouch, such as the Axum® treatment couch developed by Accuray, Inc. ofCalifornia. Alternatively, other types of treatment tables may be used.

According to one embodiment of the invention, a localization array 105may be attached to the treatment couch 104. For example, localizationarray 105 may be attached to the underside of treatment couch 104 sothat the detection field, a volume within which fiducial tracking ismost effective, of localization array 105 is directed upwards throughthe treatment couch 104 and the body of patient 103. The localizationarray 105 may be placed so that its detection field encompassesimplanted fiducial markers 106, which are implanted within the body ofpatient 103. The localization array can then be used to track themovement of implanted fiducial markers 106, and may include transmittercoils, receiver coils, or both transmitter and receiver coils for thispurpose. Alternatively, transmitter coils may be removed fromlocalization array 105, so long as the signal from the transmitter coilscan still reach the implanted fiducial markers 106. Processing unit 107may be used to collect tracking data from localization array 105 anddirect robotic arm 101 to reposition the beam of LINAC 102 according tothe most recently determined target position. The position of the targetmay, for example, be determined in reference to the implanted fiducials106 if the target has a known location with respect to the implantedfiducials 106.

FIG. 2 illustrates a treatment couch assembly including an integratedlocalization array according to one embodiment of the invention.Treatment couch assembly 200 includes localization array 201, which iscontained within treatment couch 202. Localization array 201 containselectromagnetic coils 203 which may be used for tracking of fiducialmarkers located within detection field 204. Electromagnetic coils 203may include transmitter coils, receiver coils, or a combination oftransmitter and receiver coils.

In FIG. 2, localization array 201 is exposed for clarity, although insome embodiments, localization array 201 may be concealed beneath thesurface of treatment couch 202. Alternatively, localization array 201may also be laid on top of treatment couch 202 and may or may not besecured to treatment couch 202. Whether laid on top or integrated withintreatment couch 202, localization array 201 may be covered. For example,localization array 201 may be covered to protect from physical damage orfor aesthetic reasons. The covering material may be chosen to haveminimal effect on the fiducial tracking capability of the localizationarray 201. The covering material may also be chosen for the comfort of apatient 103 or to protect the patient 103 or the localization array 201.For example, the covering may be a pad placed over the localizationarray 201. Localization array 201 may also be centered with respect totreatment couch 202 along one or more axes of treatment couch 202. Forexample, localization array 201 may be centered along the width oftreatment couch 202.

Localization array 201 may, in one embodiment, cover or underlie only aportion of the surface of treatment couch 202. Alternatively,localization array 201 may cover or underlie the entire surface oftreatment couch 202. While in one embodiment, treatment couch 202contains only one localization array 201, other embodiments of treatmentcouch 202 may contain more than one localization array 201.

During a treatment session, a patient 103 may lie on treatment couch 202so that implanted fiducial markers 106 implanted in the body of patient103 are within the detection field 204 of localization array 201.Localization array 201 may then be used to track the locations ofimplanted fiducials 106.

FIG. 3A illustrates a treatment couch assembly that includes alocalization array mounted underneath the surface of a treatment couchaccording to one embodiment of the invention. Treatment couch assembly300 includes a localization array 301 mounted underneath a treatmentcouch 302. Localization array 301 may be attached to a positioningmechanism 303 through an extension arm 304. Positioning mechanism 303may be mounted on a platform 305 attached to treatment couch 302.

Localization array 301 may be positioned underneath the surface oftreatment couch 302 so that the detection field of localization array301 extends through and above the surface of treatment couch 302.Localization array 301 may include transmitter coils, receiver coils, orboth transmitter and receiver coils. Localization array 301 may also beattached to a positioning mechanism 303. In one embodiment, positioningmechanism 303 may be mounted on platform 305. Alternatively, positioningmechanism 303 may be mounted on the underside of treatment couch 302.Platform 305 may be rigidly attached to treatment couch 302 so thatpositioning mechanism 303 does not move with respect to treatment couch302. Thus, repositioning of localization array 301 may occur solelythrough the operation of positioning mechanism 303. In alternativeembodiments, positioning mechanism 303 may be attached to treatmentcouch 302 in a manner that allows movement between treatment couch 302and positioning mechanism 303 and localization array 301. For example,treatment couch 302 may be mounted on slides that allow treatment couch302 to move along the x-axis 310 with respect to positioning mechanism303 and localization array 301. Positioning mechanism 303 may operate tomove localization array 301 with respect to the treatment couch 302. Forexample, positioning mechanism 303 may move localization array 301 alongthe x-axis 310 or y-axis 311. Thus, during a radiation treatmentsession, the localization array 301 may be moved to a desired positionso that its detection field may encompass fiducial markers being trackedwithout moving the patient or the treatment couch 302. Positioningmechanism 303 may also operate to move localization array 301 outsidethe imaging field of other imaging devices in the treatment room. Forexample, if an x-ray imager is in use, the localization array 301 may bemoved out of the imaging field of the x-ray imager so that thelocalization array 301 is not captured in the x-ray image. Localizationarray 301 may also be moved for other reasons, such as to avoidobstructing moving equipment or personnel. Positioning mechanism 303 mayalso operate to move localization array 301 in the direction indicatedby z-axis 312 in order to bring localization array 301 closer to orfarther away from treatment couch 302.

Positioning mechanism 303 may in one embodiment be implemented using anX-Y table. Alternatively, other mechanisms such as robots ornon-motorized manual positioning mechanisms may be used. Positioningmechanism 303 may also accept inputs from a computer or other device inorder to automate the movement of localization array 301 during atreatment session. Furthermore, positioning mechanism 303 may also sendsignals to another device to indicate the position of localization array301. In one embodiment, mechanical encoders are used to determine theposition of the localization array in the treatment room. For example,positioning mechanism 303 may utilize servo motors capable of indicatingthe rotational positions of the motors, which can then be used tocalculate the position of the localization array 301. Alternatively,other methods for determining the location of localization array 310 maybe used in conjunction with positioning mechanism 303, such aspositioning marks or optical sensors.

Localization array 301 may be attached to positioning mechanism 303using an extension arm 304. Extension arm 304 may be used so thatlocalization array 301 is kept away from positioning mechanism 303. Forexample, in cases where the operation or structure of positioningmechanism 303 may degrade the electromagnetic signals received bylocalization array 301, extension arm 304 may enable localization array301 to be sufficiently removed from positioning mechanism 303 so thatthe electromagnetic signals are unaffected by positioning mechanism 303.Alternatively, localization array 301 may in other embodiments beattached to positioning mechanism 303 without using extension arm 304.

FIG. 3B illustrates a treatment couch assembly where the localizationarray is positioned beyond an imaging field of an imaging deviceaccording to one embodiment of the invention. Imaging device 306 isconfigured to capture images from within imaging field 307. Imagingdevice 306 may be a device such as an x-ray imager.

Localization array 301 may be moved using positioning mechanism 303 sothat localization array 301 is positioned beyond imaging field 307. Withthe localization array 301 in this position, imaging device 306 mayavoid capturing localization array 301 in an image. For example, imagingdevice 306 may be used to capture images of a patient's anatomy whilethe patient is lying on treatment couch 302. In this case, allowinglocalization array 301 to remain in the imaging field may obscure theanatomical features which are the desired subject of the resultingimage.

FIG. 3C illustrates a treatment couch assembly having a localizationarray that is rotated beyond an imaging field of an imaging deviceaccording to one embodiment of the invention. A rotational movement mayalso be used to position localization array 301 outside the imagingfield 307 of imaging device 306. For example, positioning mechanism 303may include a swivel connection to allow positioning mechanism 303 toswing localization array 301 out of the imaging field 307.

FIG. 4 illustrates a treatment couch assembly including a localizationarray that is secured to the treatment couch using an attachmentmechanism. Treatment couch assembly 400 includes treatment couch 401having a number of attachment points such as attachment point 402, clips403 and 404, a number of positioning marks such as positioning mark 405,localization array 406, and slides 407 and 408. Clips 403 and 404 andslides 407 and 408 constitute an attachment mechanism for securinglocalization array 406 to treatment couch 401. Localization array 406has a detection field 409.

Treatment couch 401 may have a number of attachment points such asattachment point 402, where clips 403 and 404 may be attached.Localization array 406 may then be attached to clips 403 and 404. Theattachment points may be located at evenly spaced positions on bothsides of treatment couch 401. Each attachment point may also have acorresponding positioning mark such as positioning mark 405. Thepositioning marks may also be labeled with numbers or other symbols usedto identify the attachment points. Identifying attachment points whereclips 403 and 404 are attached may further facilitate determining thelocation of the localization array 406 with respect to treatment couch401. This relative location may ultimately be used to locate fiducialmarkers such as implanted fiducials 106 tracked by the localizationarray 406 with respect to the beam of LINAC 102 during a radiationtreatment session. In one embodiment, the position of the localizationarray 406 with respect to the treatment couch may be determined usingmechanical encoders. For example, the attachment points or clips 403 and404 may have sensors to indicate to which attachment points thelocalization array 406 is attached. Alternatively, if the position ofthe localization array 406 relative to the treatment couch is known, theposition of the couch in the treatment room can be determined usingmechanical encoders. For example, if the couch is movable on a track,sensors on the track can be used to identify the position of the couchon the sliders. The position of the localization array in the treatmentroom then can be determined by reference to the position of thetreatment couch.

The clips 403 and 404 may be attached to the attachment points usingfasteners. For example, hooks or screw-type fasteners may be used toattach clips 403 and 404 to the attachment points. Other types offasteners may also be used. The fasteners may be selected based on theirability to support the weight of localization array 406 and clips 403and 404. In one embodiment, clips 403 and 404 may be separate fromlocalization array 406 such that clips 403 and 404 may be attached totreatment couch 401 independently from localization array 406. In otherembodiments, clips 403 and 404 and localization array 406 may be asingle assembly to be attached to treatment couch 401 in a single piece.

Localization array 406 may be repositioned along the x-axis 310 withrespect to the treatment couch 401 by detaching clips 403 and 404, andthen reattaching clips 403 and 404 at different attachment points.Localization array 406 may also be repositioned along the z-axis 312 byexchanging clips 403 and 404 with a set of shorter or longer clips.Alternatively, clips 403 and 404 may be adjustable in length so that thesame clips 403 and 404 may be used to adjust the position oflocalization array 406 along the z-axis 312. Localization array 406 maybe equipped with slides 407 and 408 to support localization array 406 onclips 403 and 404 while allowing localization array 406 to berepositioned along the y-axis 311 relative to the treatment couch 401.Using these and other mechanisms known in the art, localization array406 may be repositioned so that its detection field 409 is in an optimalposition for tracking a set of fiducial markers.

FIG. 5 is a flow chart illustrating a process for setting up and usingan electromagnetic localization array and treatment couch assemblyaccording to one embodiment of the invention. Localization array setupprocess 500 begins with block 501, where an optimal position for alocalization array such as localization array 105 is determined. In oneembodiment, the optimal position for localization array 105 may be aposition where the detection field of localization array 105 encompassesimplanted fiducial markers 106. Alternatively, an optimal position for alocalization array may be determined based on other factors or acombination of factors. For example, the optimal position may bedetermined based on a desired characteristic of a signal received by thelocalization array 105 from the implanted fiducials 106. The optimalposition may also be chosen to avoid obstruction by the localizationarray 105 of imaging equipment or moving equipment such as robotic arm101.

After the optimal position for the localization array is identified inblock 501, execution proceeds to block 502, where positioning marks maybe used to identify an attachment location for the localization array.For example, in one embodiment, positioning marks such as positioningmark 405 may identify one or more attachment points such as attachmentpoint 402 where clips 403 and 404 may be attached so that localizationarray 406 is positioned at the optimal position. In other embodiments,positioning marks may not be required to identify an attachment locationbecause the localization array may already be attached to the treatmentcouch. For example, the localization array may be integrated into thetreatment couch, such as localization array 201, or the localizationarray may be designed to remain attached to the treatment couch betweentreatment sessions. In these cases, localization array setup process 500may not require block 502.

Following block 502 is block 503, where the localization array may beattached to the attachment location identified in block 502. Forexample, clips 403 and 404 supporting localization array 406 may beattached to attachment points identified in block 502 so that thelocalization array 406 can be positioned at the optimal positionidentified in block 501. In some embodiments, localization array setupprocess 500 may not require block 503 because the localization array mayalready be attached to the treatment couch.

From block 503, execution may proceed to block 504, where thelocalization array may be moved to the identified optimal position. Atthis stage, the localization array may already be attached to thetreatment couch. Thus, moving the localization array to the optimalposition identified in block 501 may entail using a positioningmechanism, such as positioning mechanism 303 or slides 407 and 408, tomove the localization array along one or more axes in relation to thetreatment couch.

After the localization array has been moved to the optimal position,execution may proceed to block 505, where the localization array ismaintained at the optimal position during a treatment session. Theposition of the localization array may be maintained in accord withblock 505 for only a portion of the entire treatment session. Forexample, if the fiducial markers move during the treatment session, theposition of the localization array may be adjusted to compensate for themovement before the end of the treatment session. Furthermore, thelocalization array needs only to be sufficiently stationary to allowtracking of fiducial markers. For example, processing unit 107 oranother part of the tracking system may tolerate or compensate for smallmovements of the localization array 105. The position of thelocalization array may be maintained by physically immobilizing thelocalization array with respect to the treatment couch. For example, ifthe localization array is attached to the treatment couch through apositioning mechanism such as positioning mechanism 303, the positioningmechanism may be turned off or locked in place. If the localizationarray is equipped with slides such as slides 407 and 408, then theslides may be locked, clamped, or otherwise immobilized to preventmovement of the localization array. Alternatively, the localizationarray may maintain its position without further action. For example,locking or clamping of slides 407 and 408 may not be required iffriction is sufficient to prevent undesired movement of localizationarray 406. Also, if the localization array is integrated into thetreatment couch, such as localization array 201, the localization arraymay already be immobilized with respect to the treatment couch.

While the localization array is being maintained in a known position,the localization array may be used to track locations of fiducialmarkers relative to the localization array, as provided in block 506. Ifthe position of the localization array relative to the treatment couchand the position of the treatment couch relative to other equipment arealso known, then the locations of the tracked fiducial markers relativeto other equipment may be determined. For example, the locations of thefiducial markers may be determined relative to the location of a LINACadministering radiation treatment. Block 506 may also be repeated duringthe course of the treatment session so that the location of the fiducialmarkers can be periodically updated. Thus, maintaining the localizationarray in a stable position relative to the treatment couch may eliminatethe need for recalculating or re-detecting the positional offset of thelocalization array from the treatment couch each time the locations ofthe fiducial markers are determined. Furthermore, if the localizationarray is attached to the treatment couch, the localization array maymaintain its positional offset relative to the treatment couch even ifthe treatment couch is moved during the treatment session. Anotheradvantage of maintaining the positional offset between the localizationarray and the treatment table is that the fiducial markers within thedetection field of the localization array may remain within thedetection field of the localization array even if the treatment couch ismoved. For example, implanted fiducial markers 106 within patient 103lying on treatment couch 104 may be encompassed by the detection fieldof localization array 105. If localization array 105 is attached totreatment couch 104, then patient 103, implanted fiducials 106,localization array 105, and the detection field of localization array105 may all move concurrently with treatment couch 104. Thus, thedetection field will continue to encompass the implanted markers 106even if the treatment couch 104 is moved, facilitating reliable trackingof the implanted fiducials 106. By tracking the locations of fiducialmarkers, a treatment delivery system such as treatment delivery system100 may then use robotic arm 101 to position LINAC 102 to deliverradiation to a target that can be located with reference to theimplanted fiducials 106.

FIG. 6 illustrates one embodiment of a treatment delivery system with alocalization array. Treatment delivery system 600 is configured tocompensate for positional information error in an electromagnetictracking system resulting from perturbations in the electromagnetictracking system's magnetic field. Such distortions of the magnetic fieldtend to increase error in the determination of the position of implantedfiducials by the electromagnetic tracking system. The electromagnetictracking system of treatment delivery system 600 may include aprocessing unit 107, localization array 105.

In one embodiment, the bias or offset error caused by perturbations inthe magnetic field may be initially compensated by calibrating orcharacterizing the effect of the treatment delivery system (e.g., gantrysystem or robot-mounted LINAC 102), which could for example be aone-time procedure involving precalibration and storage of distortionoffset for one or more possible positions of a gantry or robotic arm. Insome embodiments, electromagnetic disturbances caused by equipment canbe minimized by constructing the equipment from low conductivity ornon-conductive materials. For example, the treatment couch 104 may beconstructed from Kevlar. As compared to other light-weight materials,such as carbon-fiber, Kevlar is less conductive and thus tends to causeless distortion in the electromagnetic field. Nevertheless, additionalsources of magnetic field distortion may not be accounted for throughmaterial selection for the treatment couch. A possible additional sourceof error is metal implants inside a patient (e.g., hip prosthesis), forwhich changing the material of the treatment couch or precalibrating thesystem may not be feasible.

In another embodiment, an independent fiducial localization method isused in order to compute the distortion offset. The positions of theimplanted fiducial may obtained through use of an imaging system (e.g.,X-ray, x-ray computed tomography, etc.) that can localize the implantedfiducials with very high accuracy (e.g., several tenths of a millimeteror better). The difference between the imaging acquired implantedfiducial positions and the fiducial positions determined usinglocalization array 105 is, thus, the bias or offset of theelectromagnetic tracking positions. An x-ray imager is discussedhereafter for ease of explanation purposes. It should be noted againthat other imaging modalities and systems such as cone-beam CT (i.e.,x-ray imaging system rotated about the patient to generate a cone-beamCT) and ultrasound may be used.

One embodiment of an X-ray imaging system includes both an X-ray sourceand an X-ray detector panel. Treatment delivery system 600 includesX-ray sources 610 and X-ray detector panels 611. The X-ray sources 610may be mounted angularly apart, for example, about 90 degrees apart, andaimed through the treatment target (e.g., tumor within the patient)toward the X-ray detector panels 611. Alternatively, a single largedetector may be used that would be illuminated by each of the X-raysources 610. In the single detector imaging system, the X-ray sources610 may be positioned apart at an angle less than 90 degrees to keepboth images on the single detector surface.

The detector panels 611 may be placed below the treatment target (e.g.,on the floor), on the treatment couch 104, or underneath the LINAC 102,and the X-ray sources 610 may be positioned above the treatment target(e.g., the ceiling of the treatment room), to minimize magnification ofthe images and, therefore, the required size of the detector panels 611.In an alternative embodiment, the positions of the X-ray sources 610 andthe detector panels 611 may be reversed, e.g. the X-ray sources 610below the treatment target and the detector panels 611 above thetreatment target. In another embodiment, the detector panels 611 arearranged in a manner such that they move into position for imaging andare moved out of the way during positioning of the LINAC 102 or thetreatment couch 104 or during delivery of the radiation beam from theLINAC 102.

By using two X-ray imagers, which could be mounted approximatelyorthogonally, the 2D positions of the implanted fiducials 106 in theX-ray images can be back projected to obtain their 3D positions in thetreatment room. The fiducial positions obtained using x-ray imagelocalization can be known with very high accuracy (several tenths of amillimeter or better). The difference between the X-ray image-basedfiducial positions and the fiducial positions determined usinglocalization array 105 is thus the bias or offset of the electromagnetictracking positions. In one embodiment, the electromagnetic bias oroffset is calculated by processing unit 107, which may be connected tolocalization array 105 and X-ray detector panels 611. Thus, processingunit 107 may receive the locations of the implanted fiducials 106 asdetermined by the localization array 105 and as determined by X-rayimaging. Processing unit 107 may further use the calculatedelectromagnetic bias or offset in controlling robotic arm 101 to directthe beam of LINAC 102 at a treatment target.

The electromagnetic bias often changes slowly with spatial location.Thus, for small motions, the offset can be used to correct the real-timeelectromagnetic tracking positions, as determined using the localizationarray 105. Since electromagnetic tracking with the localization array105 does not involve radiation exposure to the patient, it may be usedto track the positions of implanted fiducials 106 in near real time. Theuse of electromagnetic tracking to avoid the use of X-ray imaging isdesirable because very frequent X-ray images of the patient may resultin excessive radiation exposure to the patient. Any bias in theelectromagnetic tracking positions can be corrected by taking occasionalX-ray images to locate the implanted fiducials 106 with greateraccuracy. The frequency of the X-ray images can be varied as necessary,for example, at every position of the treatment delivery system (e.g.,gantry or LINAC 102). Alternatively, X-ray images may be capturedperiodically over time. New X-ray images could also be acquired wheneverthe electromagnetic tracking fiducials move beyond a certain threshold.Note that using an X-ray imaging system also requires that the treatmentcouch (e.g., in the form of a table or chair) be relatively radiolucent.

In order to determine the fiducial positions relative to the treatmentroom coordinate system, the position of localization array 105 in thetreatment room needs to be known. The location of the localization array105 can be obtained, for example, by tracking the array with an opticaltracking system. However, this requires a line of sight between thearray and the optical system. Placing the localization array 105 underthe patient 103 is desirable for many reasons. This placement reducespotential collision issues with the treatment delivery system (gantrysystem or robotic arm 101 with LINAC 102). Placing the localizationarray 105 under the patient 103 could be accomplished by placing thearray 105 on the treatment couch 104 and placing a pad over the array105. The localization array 105 could also be integrated into thetreatment couch 104. The localization array 105 may be movable toaccommodate different patient sizes and setup positions and differenttreatment target positions. For example, localization array 105 could beplaced in a platform or housing such that it can be easily moved alongthe long axis of the table and possibly also along the short axis of thetable. Placing the array 105 under the patient 103, whether on orintegrated into the treatment couch 104, may require a non-opticalmethod for obtaining the position of the array 105 in the treatmentroom. One non-optical method for tracking the position of array 105 isto use one or more (e.g., two) X-ray imagers.

FIG. 7 illustrates one embodiment of a localization array 700 that canbe tracked using X-ray imaging. Localization array 700 includes fiducialmarkers 701 that are located outside of patient 103, and also includeselectromagnetic coils 203. Localization array 700 is integrated intreatment couch 202 so that detection field 204 encompasses an areaabove treatment couch 202.

With external fiducial markers 701 embedded in array 700, the positionof array 700 can be tracked using a tracking device such as an X-rayimager. It should be noted that the term “external fiducial markers” isused herein to distinguish from the implanted fiducials that areinternal to a patient. Accordingly, an external fiducial marker is onewhich is disposed outside of a patient's body. External fiducial markers701 may be made from a radio-opaque material so that external fiducials701 will appear in X-ray images. By using two X-ray imagers, which couldbe mounted approximately orthogonally, the 2D positions of the externalfiducials 701 in the X-ray images can be back projected to obtain their3D positions. The 3D positions are transformed to the treatment roomcoordinate system and, thus, the position of the localization array 700in the treatment room coordinate system is determined. Suchtransformations are known in the art; accordingly, a detaileddescription is not provided herein. Alternatively, electromagnetic coils203 in the array 700 could be used as fiducials to be tracked by atracking device. If the tracking device is an X-ray imager, the coilsmay be uniquely distinguishable radiographically. For example, each ofthe electromagnetic coils 203 may have a unique shape so that the coiland its position can be uniquely identified in an X-ray image. Theposition of localization array 700 could be determined with othermethods as well. In one embodiment, if the localization array 700 isintegrated into the treatment couch 202 and is movable with respect totreatment couch 202, a position tracking device may include mechanicalencoders which can be used to obtain the position of the localizationarray 700 relative to the treatment couch 202. Mechanical encoders mayalso be used to determine the position of treatment couch 202 in thetreatment room. Treatment couch 202 could be a conventional treatmenttable, or could be a table top mounted on a robotic manipulator.

Thus, the position of localization array 700 relative to the treatmentroom coordinate system and the positions of implanted fiducial markers106 in patient 103 relative to localization array 700, aselectromagnetically tracked by the localization array, can be used todetermine the positions of implanted fiducials 106 relative to thetreatment room coordinate system. In addition, bias or offset error inthe electromagnetically tracked position of the implanted fiducials 106caused by disturbances in the electromagnetic field can be corrected byusing occasional X-ray images to more accurately locate the implantedfiducials 106. This method for determining the location of the implantedfiducials 106 may be used not only with localization arrays that areintegrated with treatment couch 104, but also with localization arraysthat are not coupled to the treatment couch 104.

FIG. 8 illustrates a treatment delivery system capable of tracking thelocation of fiducial markers using a localization array external to thetreatment couch, in conjunction with X-ray imaging according to oneembodiment of the invention. Treatment delivery system 800 includeselectromagnetic tracking system 810 connected to localization array 811.Localization array 811 has a detection field 812 that extends downwardsto encompass implanted fiducials 106. Treatment delivery system 800 alsoincludes X-ray imagers comprising X-ray sources 610 and X-ray detectorpanels 611.

Localization array 811 may be similar to localization array 700, havingelectromagnetic coils that can be used to determine the positions ofimplanted fiducials 106. Localization array 811 is not attached totreatment couch 104, and thus may be moved independently of treatmentcouch 104. In one embodiment, localization array 811 is mechanicallysupported by electromagnetic tracking system 810. For example,localization array 811 may be mounted on an adjustable arm 813 connectedto electromagnetic tracking system 810, which allows localization array811 to be situated above patient 103. Accordingly, localization array811 may have a detection field 812 that extends downward to encompassimplanted fiducials 106 so that localization array 811 can track thepositions of implanted fiducials 106. Electromagnetic tracking system810 that is attached to localization array 811 may be an external unitcontaining electronics, such as drive circuitry and sensors used duringthe operation of localization array 811. Electromagnetic tracking system810 may receive fiducial positions from localization array 811, and mayfurther be connected to processing unit 107 so that the fiducialpositions can be transmitted to processing unit 107. At processing unit107, the fiducial positions can be used to control the movement ofrobotic arm 101.

Localization array 811 may also be affected by disturbances in theelectromagnetic field, such that error is increased in theelectromagnetically tracked positions of the implanted fiducials 106.X-ray imagers comprising X-ray sources 610 and X-ray detector panels 611can be used to compensate for bias or offset caused by suchelectromagnetic disturbances. By using two X-ray imagers mountedapproximately orthogonally, the 2D positions of the implanted fiducials106 in the X-ray images can be back projected to obtain their 3Dpositions in the treatment room with high accuracy. The differencebetween the X-ray image-based fiducial positions and the fiducialpositions determined using localization array 811 is thus the bias oroffset of the electromagnetic tracking positions. This electromagneticbias or offset may be calculated by processing unit 107, which receivesthe positions of implanted fiducials 106 as determined by thelocalization array 105 and the X-ray imaging system. The offset can thenbe used to correct the real-time electromagnetically tracked positions,as determined using the localization array 811. Any bias in theelectromagnetically tracked positions can be corrected by takingoccasional X-ray images to locate the implanted fiducials 106 withgreater accuracy. The frequency of the X-ray images can be varied asnecessary, for example, at every spatial position of the treatmentdelivery system (e.g., gantry or LINAC 102). New X-ray images could alsobe acquired whenever the electromagnetically tracked implanted fiducials106 move beyond a certain positional threshold.

The resulting corrected positions of implanted fiducials 106 can be usedby processing unit 107 to control robotic arm 101. Using thesepositions, processing unit 107 may direct robotic arm to aim LINAC 102so that the beam of LINAC 102 intersects a treatment target that can belocated by reference to the implanted fiducials 106.

Alternatively, treatment delivery system 100 may be a type of systemother than a robotic arm-based system. For example, treatment deliverysystem 100 may be a gantry-based (isocentric) intensity modulatedradiotherapy (IMRT) system. In a gantry based system, a radiation source(e.g., a LINAC) is mounted on the gantry in such a way that it rotatesin a plane corresponding to an axial slice of the patient. Radiation isthen delivered from several positions on the circular plane of rotation.In IMRT, the shape of the radiation beam is defined by a multi-leafcollimator that allows portions of the beam to be blocked, so that theremaining beam incident on the patient has a pre-defined shape. Theresulting system generates arbitrarily shaped radiation beams thatintersect each other at the isocenter to deliver a dose distribution tothe target region. In IMRT planning, the optimization algorithm selectssubsets of the main beam and determines the amount of time that thepatient should be exposed to each subset, so that the prescribed doseconstraints are best met. In one particular embodiment, the gantry-basedsystem may have a gimbaled radiation source head assembly.

It should be noted that the methods and apparatus described herein arenot limited to use only with medical diagnostic imaging and treatment.In alternative embodiments, the methods and apparatus herein may be usedin applications outside of the medical technology field, such asindustrial imaging and non-destructive testing of materials. In suchapplications, for example, “treatment” may refer generally to theeffectuation of an operation controlled by the treatment planningsystem, such as the application of a beam (e.g., radiation, acoustic,etc.) and “target” may refer to a non-anatomical object or area.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a computer-readable medium.These instructions may be used to program a general-purpose orspecial-purpose processor to perform the described operations. Acomputer-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a computer. The computer-readable medium mayinclude, but is not limited to, magnetic storage medium (e.g., floppydiskette); optical storage medium (e.g., CD-ROM); magneto-opticalstorage medium; read-only memory (ROM); random-access memory (RAM);erasable programmable memory (e.g., EPROM and EEPROM); flash memory; oranother type of medium suitable for storing electronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the computer-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the communication medium connecting the computer systems.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

What is claimed is:
 1. An apparatus, comprising: a treatment couch; anda localization array integrated within the treatment couch.
 2. Theapparatus of claim 1, wherein the treatment couch is a robotic couch. 3.The apparatus of claim 2, wherein the treatment couch has at least fivedegrees of freedom of movement.
 4. The apparatus of claim 1, wherein thelocalization array includes at least one receiver coil and at least onetransmitter coil.
 5. The apparatus of claim 1, wherein the localizationarray is covered.
 6. The apparatus of claim 1, wherein the localizationarray is centered within the treatment couch.
 7. The apparatus of claim1, further comprising an additional localization array being eitherintegrated within or coupled to the treatment couch.
 8. An apparatus,comprising: a treatment couch; and a localization array positioned abovethe treatment couch.
 9. The apparatus of claim 8, further comprising apositioning apparatus coupled with the localization array and configuredto allow movement of the localization array along at least one axisparallel to a surface of the treatment couch.
 10. The apparatus of claim8, wherein the positioning apparatus is further configured to allowpositioning of the localization array beyond an imaging field of animaging device.
 11. The apparatus of claim 8, wherein the treatmentcouch is a robotic couch.
 12. The apparatus of claim 8, wherein thetreatment couch has at least five degrees of freedom of movement. 13.The apparatus of claim 8, further comprising a mechanical arm coupled tothe localization array configured to move the localization arrayindependently of the treatment couch.
 14. The apparatus of claim 8,wherein the localization array includes at least one receiver coil andat least one transmitter coil.
 15. The apparatus of claim 8, furthercomprising an electromagnetic tracking system operatively coupled withthe localization array.
 16. A method, comprising: providing alocalization array in substantially an optimal position; and maintainingthe localization array at substantially the optimal position bycontrolling movement of the localization array.
 17. The method of claim16, wherein the localization array is integrated within a treatmentcouch such that the localization array is immobilized with respect tothe treatment couch and controlling movement of the localization arraycomprises moving the treatment couch.
 18. The method of claim 16,wherein the controlling movement of the localization array comprisesmoving an arm coupled to the localization array.
 19. The method of claim16, further comprising using the localization array to locate at leastone fiducial marker.
 20. The method of claim 16, wherein maintaining thelocalization array at substantially the optimal position comprisestolerating or compensating for deviations of the localization array fromthe optimal position.
 21. The method of claim 16, further comprising:determining the optimal position for the localization array; and movingthe localization array to substantially the optimal position.
 22. Themethod of claim 21, wherein determining the optimal position comprisesdetermining a position where a detection field of the localization arrayencompasses at least one fiducial marker.
 23. The method of claim 21,wherein the optimal position is based on a desired characteristic of asignal received by the localization array from at least one fiducialmarker.
 24. The method of claim 21, wherein the optimal position chosento avoid obstruction by the localization array of imaging equipment orequipment relative to the localization array.
 25. The method of claim16, wherein maintaining the localization array at substantially theoptimal position is performed for at least a portion of a treatmentsession.
 26. The method of claim 18, further comprising moving atreatment couch independently of maintaining the localization arraywherein a detection field of the localization array continues toencompass at least one fiducial marker when moving the treatment couch.